Airworthiness Directive 87-08-09 issued by the Federal Aviation Administration requires that tires on many large commercial aircraft be inflated with dry nitrogen that does not exceed 5% oxygen by volume to minimize the potential for an explosive chemical reaction between the inner tire lining and atmospheric oxygen. After tires are inflated in accordance with this directive, it has heretofore been necessary to perform a time-consuming testing process to ensure that they are not leaking or are leaking at an acceptably low rate. A conventional process for inflating and testing aircraft tires is discussed below with reference to FIG. 1 of the attached drawings.
FIG. 1 illustrates the steps involved in a conventional tire inflation and testing process. At a first step 300, a wheel is mounted so that the tire on the wheel can be inflated. At step 302, the wheel is staged in an inflation cage and hooked up to a source of pressurized nitrogen. Tire inflation is complete at step 304, and the wheel is staged in the final mechanic area at step 306. The time that step 306 is performed is documented on a tape or label, and the tape or label is affixed to or associated with the wheel at step 308.
The tire stretches during the inflation process and continues to stretch for a period of time after inflation. Therefore, many manufacturers recommend that a tire be allowed to sit for a period of time, such as one hour, before pressure measurements are taken. This is because the increasing volume of the stretching tire will cause a small pressure drop even though the tire is not leaking. The tire is allowed to stretch at step 310 for a period of one hour, and a pressure measurement is taken at step 312.
Next, the tire is checked for leaks by applying a soapy water solution to the tire and watching for the formation of air bubbles at step 314. A determination is made at step 316 as to whether the tire passes this leak test. If the tire fails, that is, if escaping gas bubbles are noted, the tire is re-inspected and/or repaired at a step 318. If the tire is not visibly leaking, the wheel is staged at step 320 for a period of 12 to 24 hours to determine whether it holds pressure to an adequate degree over this period. Industry guidelines permit up to a 2.5 percent pressure loss over 12 hours. Tire pressure is measured after 12 to 24 hours at step 322, and if the tire passes inspection, the passing pressure level is recorded at step 324. A final inspection of the wheel and tire is performed at step 326.
As will be appreciated from the above, the conventional method includes a minimum waiting period of thirteen hours after inflation to ensure that the tire is retaining pressure. Including the time required for mounting, dismounting and taking and recording measurements, the tire inspection process requires more that thirteen hours. Therefore, when an aircraft tire requires inflation or reinflation, an airline will lose the use of that tire for over thirteen hours. This is longer than the typical overnight down-time for a plane and can result in expensive delays to an airline. Thus, maintenance facilities may be required to keep on hand a supply of properly inflated tires for various aircraft and/or take other expensive steps to minimize this problem.
It would therefore be desirable to provide a method of reducing the time required to determine whether a newly inflated aircraft tire is retaining pressure to a required degree.